1. Field of the Invention
The invention pertains to a heat-insulation wall comprising at least one layer of material to limit the convection of heat, and to its application to the building of a heat-insulation device such as, for example, a heat shield.
The wall of the invention and the device which can be made with it are intended for use in insulation or heat protection against high temperatures i.e., temperatures of at least 700.degree. C.
Heat-insulation devices, also known as heat shields, are used in many fields, for example, in industry when high temperature heat sources present risks to the environment. Heat shields are also used in aeronautics to insulate the heated parts of a jet engine from the rest of the aircraft and also in space exploration vehicles to protect them when they re-enter the atmosphere.
A heat-insulation device must be reliable and efficient and, when loaded on board a vehicle, it should be as light as possible so that the efficiency of the engine is not affected by its presence and by the additional weight which it entails.
2. Description of the Prior Art
In the prior art, there are heat-insulation devices made of refractory materials which, depending on their densification, block the transmission of calorific radiation in varying degrees. The disadvantage of these devices is that their weight and bulk increase proportionately with their efficiency.
Other devices made of at least one low-density insulating material, in the form of sheets and reflecting screens, generally meet the requisite weight conditions of vehicles but also have disadvantages. It can happen that a part of the surface of the screen is subjected to temperatures that are higher than other parts, and that the screen lets through a certain amount of heat at these higher-temperature parts of its surface while working properly at other places, owing to the temperature gradient which is created in every direction through the material.
In order to improve the efficiency of the devices comprising screens of this type, walls are made in the prior art in which there is a superimposition of reflecting screens and layers of insulating materials. The role of the screens is to reflect the infra-red radiation, and the layers of insulating materials limit the transmission of heat, through convection, beyond the screens. The insulating materials are generally based on mineral or organic wool or on products with similar properties.
However, if the heat emitted locally is excessive, it can happen that the reflecting screen is destroyed and that a layer of convection-insulating material, interposed between this screen and another, is inadequate and ultimately lets through excessive radiation and, consequently, excessive heat. The invention is therefore aimed at providing remedies for these disadvantages by enabling the building of a heat-insulation wall which is light, the insulating possibilities of which are used to the maximum throughout the surface.